1. Field of the Invention
The present invention relates to a transmission, and a measuring instrument including the transmission.
2. Description of Related Art
It is known a measuring instrument including: a measuring element for measuring an object to be measured; and a moving mechanism which has a plurality of movement axes and moves the measuring element in directions of the movement axes (for example, see Japanese Patent Unexamined Publication JP-A-2005-300318).
In such a measuring instrument, the moving mechanism has a micro-motion mechanism for finely moving the measuring element in the movement axis directions. The micro-motion mechanism includes a transmission which reduces an input rotational speed and outputs the reduced rotational speed, and the measuring element is finely moved by the output of the transmission.
In a surface property measuring instrument disclosed in JP-A-2005-300318, specifically, the moving mechanism includes a column which is slidable in a certain movement axis. The measuring element is connected to the column, and moved in accordance with the slide movement of the column. The micro-motion mechanism includes: a handle which is to be rotated by the user to finely move the measuring element; a feed screw which is extended along the moving direction of the column and is coupled to the handle; and a nut which is screwed with the feed screw. The column is connected to the nut.
When the handle is rotated, the feed screw is rotated in accordance with the rotation of the handle, to move the nut. When the nut is moved, the measuring element is moved through the column. Namely, the micro-motion mechanism of the surface property measuring instrument disclosed in JP-A-2005-300318 reduces the speed by converting the rotational speed of the handle into the moving speed of the nut to thereby finely move the measuring element. In the micro-motion mechanism of the surface property measuring instrument disclosed in JP-A-2005-300318, a transmission has the feed screw and the nut, and its speed reduction ratio is determined by the pitch of the feed screw.
Further, as other type of the micro-motion mechanisms, there is known a linear action type in which a driving shaft connected to a handle is axially moved, and a measuring element is finely moved in accordance with the movement of the driving shaft.
Furthermore, there is known a worm gear type in which a gear is rotated through a worm gear connected to a handle, and a measuring element is finely moved in accordance with the rotation of the gear.
FIG. 14 is a diagram showing a micro-motion mechanism of the linear action type.
As shown in FIG. 14, the micro-motion mechanism 100 of the linear action type includes: a handle 101 which is to be rotated by the user to finely move a measuring element; a columnar driving shaft 103 which is connected to the handle 101 through a wire 102; a plurality of bearings 104 which are disposed so as to surround the driving shaft 103; and two supporting members 105 which are placed in the lower and upper sides in FIG. 14, respectively, and support the bearings 104. The measuring element is moved in accordance with movement of the driving shaft 103.
The bearings 104 are placed to abut against the surface of the driving shaft 103 in a state where the bearings are inclined by certain angle with respect to a plane perpendicular to the axis of the driving shaft 103.
When the handle 101 is rotated, the driving shaft 103 is rotated in accordance with the rotation of the wire 102, and axially moved by certain distance which corresponds to the inclinations of the bearings 104. Namely, the micro-motion mechanism 100 reduces the speed by converting the rotational speed of the handle 101 into the movement speed of the driving shaft 103, to finely move the measuring element. In the micro-motion mechanism 100, a transmission is configured by the driving shaft 103 and the bearings 104, and its reduction ratio is determined by the diameter of the driving shaft 103 and the inclinations of the bearings 104.
FIG. 15 is a diagram showing a micro-motion mechanism of the worm gear type.
As shown in FIG. 15, the micro-motion mechanism 110 of the worm gear type includes: a handle 111 which is rotated by the user to finely move a measuring element; a worm gear 113 which is connected to the handle 111 through a wire 112; and a gear 114 which meshes with the worm gear 113. A columnar shaft portion 114A having rotation axis which is the same as that of the gear 114 is formed on the gear 114.
The micro-motion mechanism 110 further includes: a bearing 115 which is opposed to the shaft portion 114A of the gear 114; a supporting member 116 which supports the bearing 115; an urging member 118 which is connected to the supporting member 116 and a fixing portion 117; and a columnar guide rail 119 which is placed between the shaft portion 114A of the gear 114 and the bearing 115 and is extended along a certain movement axis direction. The measuring element is moved in accordance with movement of the micro-motion mechanism 110.
The supporting member 116 is a plate-like member which is formed into a substantially T-like shape in a plan view. The bearing 115 is fixed to an end portion of the member which is in the right side in FIG. 15, and the urging member 118 is connected to an end portion of the member which is in the lower side in FIG. 15. In the supporting member 116, a substantially middle portion is fixed by a pin 116A, so that the supporting member is rotatable about the pin 116A.
The urging member 118 urges the lower end portion of the supporting member 116 toward the fixing portion 117. Namely, rotational force which is counterclockwise in FIG. 15 about the pin 116A is applied to the supporting member 116. Therefore, the guide rail 119 is clamped by the shaft portion 114A of the gear 114 and the bearing 115.
When the handle 111 is rotated, the worm gear 113 is rotated in accordance with the rotation of the wire 112, and the gear 114 is rotated in accordance with the rotation of the worm gear 113. When the gear 114 is rotated, the shaft portion 114A and the bearing 115 are rotated, and the micro-motion mechanism 110 is moved along the axial direction of the guide rail 119. In the micro-motion mechanism 110, namely, the rotational speed of the handle 111 is reduced by converting into the movement speed of the micro-motion mechanism 110, to finely move the measuring element. In the micro-motion mechanism 110, a transmission has the worm gear 113 and the gear 114, and its reduction ratio is determined by the number of tooth of the worm gear 113 and the gear 114.
In the transmission of the micro-motion mechanism of the surface property measuring instrument disclosed in JP-A-2005-300318, or that of the micro-motion mechanism 100, however, the axial length of the feed screw or the driving shaft 103 must be set according to the movable distance. In the case where the transmission is applied to a measuring instrument having a moving mechanism of a long movable distance, therefore, there arises a problem in that the size of the transmission is increased.
Further, in the transmission of the micro-motion mechanism of the surface property measuring instrument disclosed in JP-A-2005-300318, or that of the micro-motion mechanism 110, a feed screw must have high straightness, or the worm gear 113 and the gear 114 must be highly accurate, and hence there arises a problem in that the production cost is increased.
Furthermore, since the structure of the transmission of the micro-motion mechanism 110 is complicated, processes such as assembly and adjustment require a prolonged time period. Therefore, there arises a problem in that the production cost is further increased. When a transmission is configured by using gears as in the micro-motion mechanism 110, there is a further problem in that backlash occurs.
Still further, when a transmission is configured by using a wire as in the micro-motion mechanisms 100, 110, backlash is caused in accordance with the length and elasticity of the wire.